The invention relates to a controlled variable compression spark-ignited internal combustion engine. More particularly, the invention relates to provision for adjusting the compression ratio of such an engine during operation, preferably by control external to the engine. The invention is also directed to a system employing variable compression ratio apparatus in conjunction with a supercharger, with computerized control for maximizing efficiency and performance.
Internal combustion engines are known to achieve greater efficiency with a high compression ratio, but higher compression ratio engines have a disadvantage. When operated with an open or nearly open throttle and under heavy load, the high pressure created within the combustion chamber after ignition tends to cause a secondary post-ignition explosion, commonly know as "knock" or "spark knock". In engines of fixed compression ratio, knock is prevented at open throttle and heavy load by retarding the spark or by using higher octane fuel, among other techniques. The use of higher octane fuel increases fuel costs, and the other techniques decrease engine efficiency.
Lower compression engines suffer less from knock, and can burn lower octane fuels, such as unleaded gasoline. However, at lower throttle settings and load conditions, low compression engines are less efficient than high compression engines because of the lower peak operating temperature and pressure. Usually combustion is less complete, with more unburned fuel exhausted from the engine.
It is therefore desirable to operate at the highest practical compression ratio, which is a function of operating conditions. Keeping the engine at optimum compression ratio requires varying the compression ratio to adjust for changing operating conditions. In an automobile such changes must be made while the engine is operating.
Several prior systems have been suggested to achieve a practical variable compression ratio engine. The prior systems have been of several types. The systems of one type have utilized the pressure in the combustion chamber to adjust the compression ratio on each firing of the cylinder. In essence, the peak pressure was limited so that knocking would not occur. While the principles of these systems should prevent knocking, they cannot achieve the optimum compression ratio under conditions when knocking would not normally occur. In most such systems, some reduction of the peak pressure would take place even when the peak pressure would not have caused knocking. This results in reduction of the compression ratio below optimum.
One suggested system for using a variable compression ratio piston is disclosed in U.S. Pat. No. 2,323,742. There, a two-piece piston was held together by a central connector, with an intermediate coil spring urging the two pieces apart. One problem with this system is that the movable portions of the piston and the spring were so heavy that the pressure in the combustion chamber could not overcome their inertia with the engine operating at speeds of 4000 to 6000 r.p.m. as is typical of many conventional automobile engines. A related problem of such systems is that they were capable of varying the compression ratio in response to pressure alone, and were not capable of control responsive to the many other factors that together determine the optimum compression ratio for a given condition.
Another proposed system for adjusting the compression ratio of an engine while the engine is in operation involved auxiliary chambers and pistons which alter the size of the combustion chamber. See, for example, U.S. Pat. Nos. 2,215,986 and 2,260,982. The apparatus of these systems occupies space in the engine head which is, in comtemporary engine design, occupied by valves or spark plugs. Most of the patents concerned with this concept relate to head valve and spark plug configurations which have become obsolete.
Another system for adjusting an engine's compression ratio dynamically involved the use of engine oil to hydraulically control the upper portion of a two-part piston. A number of patents have suggested apparatus under this concept, including U.S. Pat. Nos. 4,031,868; 3,450,111; 3,311,096; 3,038,458; and 2,742,027. With these systems, engine oil was supplied to the piston from the conventional oil pump, through a channel in the connecting rod. Although this approach had merit, it did not provide the control and flexibility of the present invention described below.
The following additional U.S. patents have suggested various apparatus for use with variable compression ratio pistons: 3,704,695, 3,656,412, 3,417,738, 3,403,662, 3,358,657, 3,303,831, 3,200,798, 3,161,112 and 2,376,214.
It has long been known that supercharging can be used to increase the power output of an internal combustion engine. Under some operating conditions, an engine may be taking in the maximum charge of fuel and air for which its carburetion system is designed, without being close to a condition which would cease knocking. Thus, a larger fuel-air charge can be accommodated and burned, and this can be accomplished by increasing the manifold pressure through supercharging. The supercharging introduces a larger fuel-air charge into the cylinders, increasing the power output of the engine. Because the greater power output is achieved without a significant increase in friction and heat losses of the engine, and because the pumping losses of the engine are reduced, the engine efficiency may be improved when compared with an engine of equal power output but without supercharging.
Nonetheless, supercharged internal combustion engines, at least so far as known and practiced heretofore, have not produced markedly superior efficiency. Similarily, variable compression ratio engines suggested thus far have not proven a practical means of increasing engine efficiency. Among the objects of the present invention is to provide an improved variable compression ratio engine controllable externally to the engine so that the compression ratio can be varied and optimized according to the prevailing conditions at any time, and to optionally provide, in conjunction with such an improved variable compression ratio engine, controlled supercharging so that a considerable smaller engine may be used in place of a larger engine, with compression ratio normally at a high value but reduced under conditions of heavy load, with the fuel supercharged under load conditions such that the smaller engine can be depended upon for substantially the same power output as the conventional larger engine, thereby realizing significant savings in fuel due to smaller displacement, lighter weight and more efficient combustion under most conditions.